The term “hydromachine” comprises pumps and hydromotors, in which a hydrostatic power conversion of a fluid takes place according to the displacement principle. Such machines are therefore also called displacement machines. With the displacement principle, the space required inside the hydromachine for producing a volume flow will be reduced and expanded again during a function period.
With hydromachines, there are two different principles of action, namely rotating machines and piston machines. In rotating machines, the supply process of the fluid takes place in the circumferential direction. For example, gearwheels or vanes are used as displacement elements. Piston machines, however, have displacement elements in the form of pistons, which perform a linear movement to cause a displacement of the fluid.
The present invention relates to hydromachines of any kind and will in the following be explained on the basis of a rotating machine.
EP 1 045 147 A2 describes a hydromachine according to the displacement principle, which produces the torque on a working shaft by means of the temporal change of the geometry of pressure chambers with differently large active surfaces between a toothed ring and an eccentrically rotating gear wheel rotor. During normal operation, with slowly rotating shaft with high torque, the fluid inlet is connected with all expanding pressure chambers, and all contracting pressure chambers are connected with the fluid outlet. During high-speed operation with low torque, a recirculation of the fluid is produced by a design ensuring that a fluid amount leaving the contracting pressure chambers is led back to some expanding pressure chambers. This happens in that a valve slide can be brought into two positions on a channel plate. In a first position of the valve slide, pressure chambers are open and a recirculation of the fluid is possible, and in a second position all pressure channels are closed by the valve slide, so that no recirculation can take place.
The recirculation thus causes a deterioration of a displacement in the hydromachine with unchanged flow through the hydromachine. The transition from low-speed operation to high-speed operation can take place in one step or in intermediary steps, when the recirculated fluid rate is not led through a commutation plate but through a control plate.
U.S. Pat. No. 4,493,622 describes a hydromachine, which is controlled in dependence of a load on a working shaft. The hydromachine has the form of a displacement motor and has one or more gear wheel sets. Between a toothed ring and a motor housing, free chambers are placed on the circumference, in which mechanical springs are installed. A minimum displacement of the hydromachine exists, when the hydromachine is in a state with low torque. With increasing load on the working shaft of the hydromachine, the pressure is increased in the pressure chambers, which are facing the fluid inlet. This leads to an increase of the torque, which acts upon both a gear wheel rotor and on a toothed ring. If this torque exceeds the tension force of the springs in the free chambers between toothed ring and housing, the springs are compressed and the toothed ring performs a rotationally limited movement. This movement of the toothed ring will increase the displacement of the hydromachine, and thus also the torque on the drive shaft.
With the methods of controlling the displacement, which have been known until now, pressure fluctuations occur in the hydromachine.